Two-stroke cycle engine



Feb. 4, 1930. A. zoLLER Two-STROKE CYCLE ENGINE Filed Feb. 6, v19255 All Patented Feb. 4, 1930 l PA-'rENT OFFICE y UNITED s'rasras' ARNOLD ZOLLER, OF BERLIN, GERMANY TWO-STROKE CYCLE ENGINE Application filed February 6, 1928, Serial No. 617,418, and in Germany January 31, 4922.

My invention relates to internalcombus-- tion yengines of the two-stroke type and it is an object of my invention to provide an engine of the kind described which may be supercharged without the necessity of introducing the supercharging mixture at high pressure, To this end I so time the operation of the means controlling the exhaust of the products of combustion and the intake of 1Q freshcombustible mixture that during the expansion stroke of the piston the exhaust controlling` means,'for instance, an exhaust valve of the usual type, are opened at a given crank angle in front ofthe lower dead centre that the intake ports are opened a little later to admit a charge of mixture which expels the exhaust gases and scavenges the cylinder,

that the exhaust valve is closed at, or sub-v stantially at, the lower dead centre of the piston, finishing the scavenging period, and

that the intake ports are closed on the compression stroke whenthe piston has moved through a given angle past its lower dead -centre position. 4'During this part of the stroke, more mixture is admitted for supercharging the engine. With this operation the products of combustion are released on the expansion stroke'when the piston is at a given distance from the lower dead centre. Shortly afterwards the intake ports are opened, for instance, laid open by the piston, so that fresh mixture enters the cylinder and expels the exhaust ases. Before, however, the top stratum of resh mixture has arrived at the '35 exhaust port, the exhaust valve is closed while the intake ports remain open. In this manner sufcient time 1s available for'eecting the required superchargingy and a comparatively low pressure in the mixture .suices vfor in- 40=troducing the mixture into the cylinder becausethe piston onf'its return stroke has onlyl moved through a comparatively small angle when the intake ports are closed so'that the compression pressure in front of the piston is insignificant and is overcome by a correspondingly low-pressure of the inflowing mixture. v u

With two-strokeinternal combustion engines in which valves are' not provided but the intake and exhaust ports are both conis the exhaust trolled by the piston it is necessary that the exhaust ports\ should be laid open before the intake ports\are opened 'and therefore lthe exhaust ports must be considerably longer than the inlet ports. In practice the length 65 of the exhaust ports is about one-fifth of the piston stroke so that the piston-swept volume of the -cylinder isreduced correspondingly. It has been attempted to overcome this draw back by providing a separateintake valve so that the length of the exhaust ports is no longer a function of the length of the intake ports. In both cases, however, the controlof the exhaust ports by the cylirfder generates a comparatively high pressure in front of the piston as the fresh mixture can only be introduced after the piston has closed the exhaust ports on .its compression stroke, whereas in my engine fresh mixture is admitted at a point considerably in advance of the lower dead centre and when practically atmospheric pressure obtains in the cylinder, and the intake period is finished about at the time when the mixture is injected in an engine of the usual type.

Fig. 1 is a transverse section of an engine havin a normal poppet exhaust valve at the top o its cylinder,

Fig. 2 is a transverse section of an engine having a rotary exhaust valve at the top of its cylinder,

Fig. 3 isa detail of the rotary exhaust valve illustrated in Fig. 2, showing part of its barrel developed and on a larger scale,

Fig. 4 is a transverse section of a modified 85 rotary exhaust valve, also drawn to a larger scale, and

Fig. 5 is a transverse section of an engine in which a rotary exhaust valve is arranged at the bottom instead of the top of the cylinder.

Referring to the drawings, 1 is the cylinder,

2 the piston, 3 the piston rod, 4 the crank circle with the centre O; 5 is the water jacket of the cylinder, and 6 the crank case. E is 95 the intake passage for the char e, and A. c passa e.v 3A. is t at crank positionl at 4which t e exhaust ports 4 are opened and A z is 'that vcrank position at which, the exhaust Vports are closed. `E is 10.

that crank position at which the intake ports are opened, and E is that position at which the admission ports are closed.

The exhaust passage A is arranged 1n the cylinder head and the admission passage E `1s situated at the lower end of the cylinder. The exhaust is controlled by a mechanically operated valve 8, 18 is the cam shaftl which is actuated by a vtoothed wheel gearmg and acts on the rod 17 controlling the exhaust valve 8; the passage 9 which communicates with the intake ports E, is controlled by the piston 2. Scavenging air or charging a1r,\or the fuel-air mixture and supercharging air, may be -supplied through the port 9. The exhaust commencesmfat the crank position the admission at the crank-position O-A. The charging may take place from said latter position to the closing of the admission channels by the piston, and the mixture supplled may have any desired pressure according to existing conditions. The directions of motion of the exhaust gases of the piston and of the charge are the same whereby scavenging losses by eddies, backing up, as well as losses in energy, are obviated and a good degree of admission is attained. Alsoit the ports 9 are elongated in order to increase the supercharged, nothing of the cylinder volume gets lost, for the mixture is further supplied until the piston has covered. said ports 9.l

A similar engine is illustrated in Figure 21, the difference being that the exhaust ports are controlled by a balanced rotary valve 11 devised for large sectional areas and high numbers of revolution. Said rotary valve 11 communicates with the combustion space through the channels 10, which terminate at two oppositely located points in such a manner that the pressures there exerted balance each other whereby a heavy lload upon the rotary valve and quick Wear and tear are obviated and the power required is diminished.` The gases passing into the bore of the rotary valve 11 may either be conducted away into the atmosphere through that bore itself in axial direction, or maybe led into the exhaust branch by means of ports 13 located laterally with respect to the head of the respective cylinder (Figure 5). lVith motors with a plurality of cylinders the exhaust ports 12 of one cylinder may form substitutes for the ports 13 of another cylinder, for instance, in the case of a six-cylinder motor where the number and distribution of said ports is such that always a sufficient number of exhaustbranches 14 coincide so that a suliicient sectional area for the exhaust is at disposal.

The importance of the rotaryvalve consists therein that in the case of a very high number of revolutions the manner of operaftion of spring-loaded and correspondingly large valves of the normal puppet type does no morel appear suilicient as extraordinary springpressures arise, so that the reliability axial valvesll al 11" might be provided as. shown in Fig. 5,' and rotated in opposite d1- rections by any suitable means. With this construction the ports 12 and 12" of the two valves are closed more rapidly and, besides, each concentric part rotates only at halt' the number of revolutions required for a single rotary valve. A constructional advantage of the concentric valves is that the ports are not controlled by the edges of the corresponding ports 10 in the cylinder casting but vby the edges of the ports 12 and 12 themselves so that it is not necessary to machine the inside of the casting in which the two valves are rotatably arranged.

In the modification illustrated inY Figure 4, the-exhaust ports, as well as the intake ports, are arranged in the lower part of the cylinder. The exhaust ports are controlled by a rotary valve 11 which is similar to the valve 11 illustrated in Fig.'3 and may also be combined from two coaxial valves as shown in Fig. 5. The corresponding crank positions are again marked A', E', Af', E.

The arrangement of the be such that the trols the exhaust E (Figure 7).

uncovering of the intake ports commences atV the crank position E o in the lower dead centre and the covering ot' the exhaust ports (A) commences simultaneously therewith.

With .all these arrangements the cam shaft 18A for the valves, or the driving shaft for the rotary valves, may be adjustable whereby it is rendered possible to increase or reduce the degree of admission, charging and the duration ofthe exhaust and intake periods, asdesired. Devices of this kind are well known in the art to which this vinvention appertains and therefore are-not illustrated'.

I now revert to Figures 1 and 2 to treat more in detail the manner of operation of the nnproved two-stroke engine, and I assume that in the present instance it is intended to supercharge the cylinder with a volume of mixture which is equal to twice the cylinder volume.

In the position illustrated, the crank is at an angular distance of about 50 degrees from its lower dead centre'radius O A and the piston is about to open the intake ports 9. This position is indicated by the radius O E. The exhaust valve 8 has been opened at a crank angle of .about 70 degrees from the radius O A as indicated by the radius O A',

the degree of superthat is, the opening of the exhaust valve 8 leads the opening of lche intake ports 9 for about 20 degrees. lVhen the exhaust valve 8 opens the pressure in the cylinder is very soon reduced to atmospheric. When the piston continues its downward stroke the intake ports 9 are completely opened and the mixture enters the cylinder, flowing toward the exhaust port A and expelling the exhaust gases. In order to prevent loss of mixture,

v theexhaust valve 8 should be closed before any mixture is able to attain the exhaust port A. When the exhaust valve. 8 has been closed which is generally effected at or about the dead centre position O A, the scavenging period is finished. The piston now starts for its compression stroke and gradually reduces the free area of the `intake ports 9 which it finally closes in the position ot' the radius O E, that is, at a crank angle of about 50 degrees to the left ofthe lower dead centre position O A. In this manner the scavenging and supercharging of the cylinder is effec-ted without any loss in the cylinder. This scavenging and superchargin g period which, with a high-speed engine, extends over about 50 degrees, according to the number of revolutionsv and the size of the engine, requires therefore the closing of the exhaust at or' about at the lower dead centre. The closing -of the exhaust ports depends also upon the desired supercharge and the pressure of the mixture. After the exhaust has been closed readily occur to a person skilled in the art.

I claim A `two-stroke cycle engine comprising a cylinder, a single acting piston movable in said cylinder, an intake port and an exhaust port in said cylinder, means for controlling said intake port, and separate means independent of said p1ston for controllingsaid exhaust port, said separate means comprising a valve with an axial bore, lateral ports 13 acting as a second exhaust passage around the circumference of said valve, a port 12 connecting lwith the axial bore of said valve, said port lalso communicating with the combustion chamber of the cylinder, and to close said exhaust port near the lower dead centre position of said piston and before said intake port is closed.

In testimony whereot` I affix my signature.

ARNOLD zoLLER.

at the lower dead centre, the intake ports 9 remain open for a given period which is determined by the degree of supercharging desired. If, as in the present instance, the degree of superch'arging is 100 per cent and thel engine is i'n'an air-plane at an altitude of about 15,000 feet the angle which the radius O E includes with the O A ot the deadl centre position should be about 50 degrees as shown in Fig. 1. lVith the large areas laid open for the inflowing mixture there is ample time for attaining the desired degree of supercharging even at maximum number of revolutions and vat the same time, the. power input to the super'chargng compressor is a minimum on account'of the low pressure obtaining in the cylinder. In the example illus- Y trated the scavenging period and the supercharging period both correspond to a crank angle of 50 degrees. It will be understood' that obviously these angles are only given by 

